In publication DE 10 2011 080 065 A1, an electromagnetic actuator is disclosed which is suitable for driving electrical switching mechanisms. Drives according to publication DE 10 2011 080 065 A1 consist of electromagnets having armatures which can also be driven electrodynamically, particularly close to the stroke initiation position—that is, with the working air gap wide open. This is achieved by means of at least one coil which is mechanically connected to the armature, and to which a force is applied by interaction of a magnetic excitation field with its current, wherein said force can be transmitted to the armature and thereby push the same in the direction of its stroke end position (closed working air gap).
The publication DE 10 2011 080 065 A1 discloses several embodiments, wherein those which have coils which are arranged coaxially (thin coils) in pairs on the frame and the armature are particularly suitable for driving electrical switching mechanisms. In the publication DE 10 2011 080 065 A1 these coils which are attached to the frame are termed “supporting coils”, and the coils which additionally drive the armature and are functionally assigned to the supporting coils are termed “thrust coils” (in this case, thrust coils are typically wound [in] the circumferential grooves of the armature). Thrust coils and supporting coils are arranged coaxially, and the thrust coil partially plunges into the supporting coil when in the stroke initiation position. If at this point the thrust and supporting coils are fed current with opposing polarity, a repulsive interaction occurs between the same, additionally driving the armature.
It is characteristic for the arrangements described that under certain conditions, very large volume-specific forces can be developed, while the inductance (for example, given a series connection of both coils) can be very small compared to conventional electromagnets. With sufficient attenuation of the eddy currents in the frame and armature, it is then possible to achieve extraordinarily high rates of force increase.
The embodiments already known from the publication DE 10 2011 080 065 A1 have two disadvantages, however: poor scalability and high transverse forces on the armature. “Poor scalability” in this context primarily means that, when the drive is designed for greater maximum forces, strokes, and particularly holding forces (against a return spring, for example), the mass of the armature is greatly increased. The armature mass increases approximately as the square of the desired nominal holding force. This makes drives according to the embodiments illustrated in DE 10 2011 080 065 A1 less well suited as replacements for, by way of example, the conventional spring drive mechanisms in large high-voltage circuit breakers. In addition, the embodiments mentioned above also demonstrate high (maximum) transverse forces during operation, which are exerted on the armature as the result of unavoidable manufacturing inaccuracies, as well as (elastic) deformations, etc., thereby placing loads on the bearing of the armature.
The problem addressed by the present disclosure is therefore that of identifying an arrangement which is more scalable, and which has much lower transverse forces than the drives known from DE 10 2011 080 065 A1.
The problem named above is addressed by an electromagnetic linear drive according to the features and structures disclosed herein.
Accordingly, a scalable, highly dynamic electromagnetic linear actuator with limited stroke is described below. The linear actuator is characterized by low transverse forces. According to one embodiment, the linear actuator comprises the following:                a stator which has two soft magnet arms;        an at least partially flat armature made of soft magnet material, which is arranged in a manner allowing movement along an axis between the arms of the stator;        at least two flat coils with a soft magnet core and high winding depth, which are attached to the stator (stator coils), wherein the coil cores are part of the soft magnet arms or are conductively connected to the same;        at least one flat coil (armature coil) with a soft magnet core and high winding depth, which is attached to the armature, wherein the coil core can be part of the armature and/or formed from the same, or the armature coil is positioned, with its soft magnet core, lying in a recess of the flat armature;        a well-defined stroke initiation position and stroke end position (“end positions”);        at least one switchable means which is designed to hold the armature in at least one end position against a return force—by way of example, a magnetic latching solenoid which is mechanically connected to the armature, or a mechanical latch;        a switchable power supply consisting of an energy storage device, such as a capacitor bank, and at least one switch.        
The armature and/or the stator arms can be made of laminated sheet packages or plastic-bonded soft magnet powders.
“At least partially flat armature” in this case means that at least the part of the armature which plunges into the stator—that is, between the arms thereof—is flat: The distance between the stator arms, and therefore the gap G in which the armature can move (with the least possible residual air gaps), is substantially smaller than the depth O (width) of the armature (and the arms, perpendicular to the gap and perpendicular to the direction of movement), and also smaller than the longitudinal extension of the armature along the movement direction. For example, the width O of the (rectangular) armature is at least three times as large as the gap G—that is, the normal distance between the stator arms. According to one embodiment, the width O is at least five times, in particular at least ten times, as large as the gap G.
The “flat coils” according to the present disclosure are flat to the extent that the length L of each (along the coil axis) is much smaller than the smallest outer diameter thereof. “High winding depth” in this context means that the height of the winding window H (along the direction of movement) lies in both the order of magnitude of the (nominal) stroke S and in the order of magnitude of the longitudinal extension K of the soft magnet coil cores along the movement direction—by way of example H=⅔*S. A “winding window” is the region of the coil which is filled with copper during operation, through which current flows. Therefore, a coil with a symmetric construction has two equally long winding windows, with a spacing (normal to the coil axis) which corresponds to the width K of the coil core. The dimension of the winding window along the longitudinal axis (normal to the coil axis) of the linear actuator is termed the winding depth H.
As mentioned, a flat coil is generally a coil wherein the smallest external dimension (twice the winding depth plus the smallest outer dimension of the core) thereof is greater than the length thereof. According to one embodiment, the winding depth H is at least two times as large as the length L of the coil (along the coil axis). According to a further embodiment, the winding depth is at least three times as large—and by way of example at least five times as large—as the length L of the coil.
The drive is, with respect to the geometry of all parts experiencing electromagnetic force densities (the (soft) magnetic and electrical parts) which must be taken into account, characterized by having essentially two mutually perpendicular mirror planes (planes of symmetry) oriented parallel to the direction of movement, the line of intersection of which (which is also the longitudinal axis) is therefore an axis of rotation with two symmetry points, running parallel to the movement direction. (The armature is mounted on the stator arms in a manner allowing sliding; and the armature and stator therefore form a glide bearing or are equipped with such a bearing.)
The result of this symmetric configuration is that the stator coils are attached to the stator arms in pairs: for each first flat coil attached to a first arm, there is a second flat coil attached on the second arm paired with the same. These stator coils must—similarly to a Helmholtz coil—be able to be fed current in the same direction, wherein according to the present disclosure both coils are able to generate the most identical possible magnetic flux during operation (which can be easily achieved by using stator coils which are as identical as possible, connecting the same electrically in series). With current flowing through the stator coils in the same direction during a switching operation, magnetic flux (primary circuit) arises from the core of a first stator coil, passes through the flat armature lying in the gap, and optionally the armature coil(s) transversely, and enters the core of the second stator coil. (The same applies to the second stator coil; the division of the coils into the first and second stator coil is arbitrary due to the symmetric configuration.) The magnetic flux returns via the arms and armature. To drive the armature from the stroke initiation position into the stroke end position (ON switching operation), current is fed to the armature coil(s), which is/are between the stator coils, in the opposite direction as the stator coils, in such a manner that they generate a flow (in amplitude) which is as identical as possible with that of the associated stator coils together. According to the present disclosure, the current is supplied at such a level that during an ON-operation, soft magnet material situated between the armature and stator coils is magnetically saturated, and it is possible to achieve a flux density locally which exceeds the saturation polarization of the material.
The stator arms and the armature are designed in such a manner that the magnetic field generated by the stator coils and armature coil(s) does not flow through any appreciable air gap. However, a very small air gap could result from manufacturing inaccuracies.
In the stroke initiation position the armature coil(s) is/are not arranged coaxially to the corresponding stator coils, but rather pushed toward the stroke end position (for example, by a half-winding depth 0.5*H); according to the present disclosure, therefore, current can be fed to all coils such that the armature and stator coil(s) repulse each other along the axis of movement in the stroke initiation position, wherein the force acting on the armature coil(s) is transmitted by the same to the armature, driving the same towards the stroke end position. An (additional) attractive force can be generated for the return to the stroke initiation position by feeding current in the same direction to all armature and stator coils(s).
In the figures, reference numbers which indicate the same or similar components with the same or corresponding meaning are the same.